The formation of very minute patterns is needed in the manufacture of recent LSI (Large-Scale Integration).
In order to enhance the faithfulness of patterns after transfer onto semiconductor substrates (wafers), usually an OPC (Optical Proximity Correction) process is performed in the manufacture of the recent LSI. With the OPC process, design data indicative of a figure is transferred onto a wafer and the figure on the wafer is transformed into a shape indicated by the design data.
In order to perform the OPC process, various methods are used according to accuracy needed. With a model-based OPC process generally used for forming recent minute patterns, a figure after the OPC process is determined by simulation.
The figure determined by simulation is an ideal value calculated by computation. Therefore, when manufacturing data is actually generated, a segment (side) obtained from the ideal value may be a segment (hereinafter referred to as an “off-grid segment”) which is not on a grid. In this case, it is necessary to rearrange (round off) the segment on the grid.
In addition, if a process in which input data and output data differ in grid is performed in pattern data processing other than the OPC process for manufacturing semiconductor devices, an off-grid segment may appear.
A method for arranging an off-grid segment which appears on a grid specified by a user for the purpose of arranging it on a grid is known (see, for example, Japanese Laid-open Patent Publication. No. 2000-100688).
Furthermore, a method for arranging an off-grid segment on a grid by making a grid finer is known (see, for example, Japanese Laid-open Patent Publication. No. 62-043778).
If an off-grid segment is arranged on a grid, usually the following method is used. The amount of deviation between the off-grid segment and the grid is determined. There are two grid lines adjacent to the off-grid segment. The off-grid segment is arranged on one of the two grid lines which is closer to the off-grid segment so that the amount of deviation between the off-grid segment and a segment obtained by arranging the off-grid segment on the grid will be minimized.
FIG. 10 illustrates a method for arranging an off-grid segment on a grid.
Points for visually confirming the grid are indicated on the grid at determined intervals. In addition, the symbols A1 through A4 for identifying columns of the grid and the symbols B1 through B3 for identifying rows of the grid are indicated.
In FIG. 10, left-hand and right-hand sides of a rectangle 91 are not arranged on the grid and are off-grid segments.
A virtual line A12 is virtually drawn midway between the column A1 (hereinafter referred to as the “grid line A1”) and the grid line A2. The left-hand side of the rectangle 91 is on the grid line A1 side from the virtual line A12.
A virtual line A34 is virtually drawn midway between the grid line A3 and the grid line A4. The right-hand side of the rectangle 91 is on the grid line A4 side from the virtual line A34.
Therefore, if the method disclosed, for example, in Patent Document 1 is used for rearranging the left-hand and right-hand sides of the rectangle 91, then a result illustrated in FIG. 10B is obtained. In FIG. 10B, left-hand and right-hand sides of a rectangle 92 are arranged on the grid lines A1 and A4 respectively.
As a result, line width between the left-hand and right-hand sides before the shift differs from line width between the left-hand and right-hand sides after the shift. That is to say, a maximum error of distance between grid lines (=(distance between grid lines×0.5)×2 (number of sides)) is produced.
In recent years, however, the requirement of an error in line width has been very severe, so it is necessary to make an error in line width smaller than or equal to distance between grid lines.
Furthermore, if the requirement of an error in line width is met by making a grid finer as disclosed in Patent Document 2, data capacity or data processing time increases and a bad influence is exerted on efficiency.